1. Field of the Invention
The present invention relates to a preloader for use in a webbing retractor or the like and adapted to allow a webbing to be applied to a vehicle occupant with appropriate tightness at the time of an emergency situation of a vehicle, i.e., at the time of a sudden deceleration of the vehicle.
2. Description of the Related Art
A seat belt apparatus is so arranged as to restrict a vehicle occupant by means of a webbing at the time of a sudden deceleration of a vehicle. If there is a large gap between the webbing and the occupant, however, it is impossible to sufficiently achieve the restraining performance. For this reason, there is a webbing retractor which is integrally provided with a preloader for allowing the webbing to be fitted closely around the occupant by forcibly pulling the webbing in the direction of retraction at the time of a sudden deceleration of the vehicle.
The preloader is actuated by a high-pressure gas generated suddenly by a gas generator filled with an explosive or the like.
At the time of a sudden deceleration of the vehicle, it is necessary for the preloader to pull the webbing with an appropriate force to cause the webbing to be fitted closely around the occupant. With the above-described conventional preloader, however, since the preloader is actuated by high-pressure gas produced suddenly by a gas generator provided with an explosive or the like, it is difficult to set the driving force of the preloader to an appropriate level. That is, if an attempt is made to cause the webbing to be fitted around the occupant with sufficient tightness, the webbing is pulled further than the state in which the webbing is fitted closely around the occupant with an appropriate fitting force. Accordingly, the webbing is fitted around the occupant with an excessive fitting force, thereby imparting discomfort to the occupant. Meanwhile, if an attempt is made to prevent the webbing from being pulled excessively, it becomes impossible to secure sufficient fitting force of the webbing with respect to the occupant owing to a shortage of gas pressure.